The basic requirements of an acceptable prosthetic foot are that it will provide a stable support for the amputee throughout a reasonable range of activities and permit the amputee to walk with a normal stride. To achieve this normal stride, the prosthetic foot must flex during walking as the foot continually moves through the heel-strike, foot-flat, and toe-off cycle. It must also, throughout this cycle, provide transverse stability particularly at toe-off, when the entire weight of the amputee is applied to the forward portion of the prosthetic foot. Prior art prosthetic feet typically are substantially transversely inflexible which interferes with side to side balancing when walking on uneven surfaces. Unlike the natural foot, these types with this unevenness and an unanticipated sideways tilting of the foot at toe-off results in an imbalance at a critical portion of the stride.
Amputees are no longer satisfied to sit in a wheelchair or to be content with a stilted, unnatural walking motion. An amputee often strives to duplicate physical activities which were conducted before the amputation. These activities may include rigorous physical activities such as running, playing basketball, and dancing.
In order to be commercially acceptable, prosthetic feet must duplicate the motions of the natural foot as much as possible. These motions include side to side stability at the toe section of the foot where weight can be exerted on each side of the foot. The ankle joint must have torsional flexibility transverse to the up and down motion of the ankle which pivotally lowers and raises the foot.
The added torsional motion of the joint in the artificial foot adds a degree of stress on the resilient pads located between the members of the artificial foot which are not otherwise present in a foot that has limited motion in only the up and down direction relative to pivotable raising and lowering of the foot.
Modern, high-tech, prosthetic feet strive to more accurately replicate the function the natural foot. In order to achieve this end, the designs of these artificial feet include more and more moving parts which impacts on the reliability and aesthetic properties of the prosthetic foot assemblies. Because of the unusually high loads imposed on the joints of prosthetic foot, compressive elements such as bumpers and cushions are subject to fatigue and are prone to failure. Accordingly, it would be desirable to have a bumper or cushion design which increase the reliability of a prosthetic foot assembly while decreasing the frequency of maintenance required to maintain the prosthetic foot assembly. Additionally, it would be desirable to have bumpers or cushions which not only have extended life, but have improved dynamic characteristics (user satisfaction).
Again, related to the aesthetics of prosthetic feet, amputees do not wish to call attention to themselves by making noise as they walk. Complex prosthetic foot designs, over thousands of load cycles, can commonly cause noises as the amputee walks with the prosthetic foot assembly. Even those amputees who do not wear cosmetic covers and feel comfortable with the "high-tech" look of their artificial limb components do not appreciate the noise generated by their prosthetic devices which can be a mental distraction. Accordingly, it would be desirable to have a prosthetic foot assembly in which noise can be eliminated to make the prosthetic foot assembly which is both aesthetically and functionally more pleasing to the wearer.
In attempts to make prosthetic foot assemblies which function more like a natural foot, very complex, multi-axis assemblies have been designed. However, these designs are costly and, therefore, can exclude segments of amputees from obtaining these more functional prosthetic devices. Accordingly, it would be desirable to have a more economical prosthetic foot assembly which provides many of the benefits of multi-axis prosthetic foot assemblies while having only one pivotal axis.